Field effect transistor-based bimolecular sensor employing a Pt reference electrode for the detection of deoxyribonucleic acid sequence

We have fabricated field effect transistor (FET)-type biomolecular sensor for the detection of the deoxyribonucleic acid (DNA) sequence based on 0.5 mum standard complementary metal oxide semiconductor (CMOS) technology and investigated its electrical characteristics. A Pt reference electrode with improved performance was employed for the detection of the DNA sequence and Au, which has a chemical affinity with thiol by forming a self-assembled monolayer (SAM), was used as the gate metal in order to immobilize the DNA. It was fabricated as a p-channel metal oxide semiconductor (PMOS) FET-type because PMOSFET with positive surface potential could be very attractive for detecting negatively charged DNA from the view point of high sensitivity and fast response time. The FET-based biomolecular sensor can detect the DNA sequence by measuring the variation of drain current due to a biomolecular charge after DNA probe immobilization and variation of capacitance after DNA hybridization. The gate potential of the sensor was applied by the Pt reference electrode and DNA was detected by both in situ and ex situ measurements. The drain current increased when a single-stranded DNA (ss-DNA) with thiol was immobilized because the effect of DNA charge with thiol is dominant. The drain current decreased when the DNA was hybridized into a double-stranded DNA (ds-DNA) because of the decrease in capacitance due to DNA hybridization. In situ measurement showed good agreement with ex situ measurement.